What is required to differentiate magnetic north from south?

Assuming I simply have some random magnets laying around, I don't believe it's possible to differentiate north from south (if I'm wrong, then my question becomes "why?"). I think I could apply an arbitrary designation to each of the poles, and then use that first arbitrarily labelled magnet to label the rest. I'd get it right 50% of the time.

What additional, minimal items would be required to determine which pole was north or south? The answer should be able to yield magnets who's labeling matches magnets on Earth. Assume that an outside magnetic field is weak or unknown (or you're not on Earth).

I guess it might be possible to use a length of wire and an ammeter to measure current direction, but that may not be the easiest manner.

You don't need an ammeter. If you have a battery and a piece of copper wire, you can hook them up, and you know that current is flowing from $$+$$ to $$-$$ on the battery. Then you can determine which way the magnet wants to align based on the field generated by the current in the wire.